Patch antennas or what are known as microstrip antennas are sufficiently well known. They conventionally comprise an electrically conductive base, a dielectric carrier material arranged thereabove and an electrically conductive radiation face provided on the upper side of the dielectric carrier material. The upper radiation face is generally stimulated by a supply line extending transversely to the aforementioned planes and layers. The connection cable used is usually a coaxial cable, the outer conductor of which is electrically connected to the ground conductor at a terminal, whereas the inner conductor of the coaxial cable is electrically connected to the radiation face located at the top.
Multilayer antennas of planar construction have, for example, become known in the form of what are known as stacked patch antennas. This type of antenna allows the bandwidth of such an antenna to be increased or resonances to be ensured in two or more frequency ranges. Antennas of this type may also be used to improve the antenna gain.
The prior publication IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. AP-27, NO. 2, MARCH 1979, pages 270 to 273, describes a multilayer patch antenna allowing resonance in two frequency ranges. The patch antenna accordingly has, for example, in addition to the bottom ground face and the radiation face arranged offset with respect thereto and stimulated via a supply line, a patch face arranged above, and laterally offset with respect to, the radiation face. The carrier material between the ground face and the radiation face and also between the radiation face and the patch face located thereabove consists, in each case, of a substrate having a uniform dielectric constant.
A patch antenna comprising carrier layers having different dielectric constants has become known, for example, from the prior publication IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 47, No. 12, DECEMBER 1999, pages 1780 to 1784. Foam is used as the upper carrier layer for the upper metallic face (patch face). The distance between the upper patch face and the radiation face located therebelow corresponds to the distance between the radiation face and the lower ground face.
The prior publication IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 47, No. 12, DECEMBER 1999, pages 1767 to 1771, among other documents, demonstrates that antenna gain may be increased using multilayer patch antennas.
Finally, a generic antenna having a multilayer construction has become known, for example, from U.S. Pat. No. 5,880,694 A. The antenna comprises a lower ground face, a dielectric carrying member located thereon and having a radiator face located on its upper side. Above the radiator face there is arranged a further dielectric member on which there is provided, on the side remote from the lower ground face, an electrically conductive patch face.
A drawback of all previously known antenna arrangements of this type is the comparatively complex construction. For, in the use of conventional commercial patch antennas having a ground face, an electric carrying member (substrate) located thereon and a radiation face located thereabove, it is invariably complex to supplement an antenna of this type to form a multilayer antenna. Depending on the use of conventional commercial patch antennas, which comprise at least a lower ground face, a substrate made from a dielectric material, for example ceramics, and a radiation face located thereon, a dielectric carrier layer, possibly of variable thickness, would then have to be produced in each case and, for example, positioned and secured on the radiation face of the conventional commercial patch antenna in order then to arrange the electrically conductive patch face on the upper side of this additional dielectric carrying layer. A different, but also highly complex, construction would involve, for example, equipping an antenna housing, below which a conventional commercial patch antenna is integrated, with an additional electrically conductive patch face; however, this would also require complex additional constructional measures.
The exemplary illustrative non-limiting implementation provides an improved multilayer antenna of planar construction, in particular a patch antenna, which, to achieve the electrical characteristics known per se, is provided with a patch radiator provided above the radiation face and which is also of simpler overall construction and/or has improved electrical characteristics.
The solution according to exemplary illustrative non-limiting implementations allows numerous advantages to be achieved.
A basic non-limiting advantage (and one that is highly surprising) is that the exemplary illustrative non-limiting antenna has significantly improved antenna characteristics compared to simple, normal patch antennas. This is all the more surprising in view of the fact that the radiation structure provided at the very top of the patch antenna is arranged at an extremely small distance above the radiation face of the patch antenna and may therefore, in an exemplary illustrative non-limiting implementation, even have longitudinal and transverse extensions which are greater than the radiation face located therebelow. After all, in such a case, the uppermost patch face would be expected adversely to influence the radiation pattern.
A further basic advantage of the exemplary illustrative non-limiting antenna is that conventional commercial patch antennas having a ground face and a radiation face and a dielectric located therebetween—preferably, for example, what are known as ceramic patch antennas—may be easily used without having to be constructionally altered. All that is required is to fasten the three-dimensional electrically conductive structure of the uppermost patch face to a conventional commercial patch antenna using a suitable adhesion and/or fastening layer.
In other words, an additional carrier structure or hood is not required in order to hold this patch face.
In an exemplary illustrative non-limiting implementation, an adhesion layer, in the form of a double-sided adhesive tape or in the form of a comparable adhesion means, is used as an adhesion structure between a conventional commercial patch antenna and the uppermost conductive three-dimensional patch element, allowing simple fastening of the uppermost patch element to a conventional patch antenna.
In an exemplary illustrative non-limiting implementation, the distance between the three-dimensional patch element and the radiation face of a patch antenna is greater than 0.5 mm, in particular greater than 1 mm, for example about 1.5 mm. Although the distance may be even greater, such a small distance between the three-dimensional patch element and the radiation face of a multilayer patch antenna is, in principle, entirely sufficient.
The three-dimensional structure of the patch element may, for example, be provided by what is known as a volume member which, in addition to its two-dimensional extension (comparable, for example, to conventional metal plates or metal layers), also has a significantly greater height or thickness of one or more millimeters.
However, alternatively, it is also possible, for example, for a three-dimensional patch element of this type, arranged above the radiation face, to be equipped with a wholly or partially peripheral edge or web edge, providing effectively a three-dimensional structure. This opens up the possibility for the patch element provided with a three-dimensional structure to be formed by a metal sheet or punched part in which edge portions, which revolve from a two-dimensional element and are oriented transversely and preferably perpendicularly to the plane of the patch element, are upwardly positioned. In the corners, the individual flange or edge portions do not necessarily have to be electrically or electrogalvanically connected to one another. The given electrical connection of a positioned edge element to an adjacent edge element is provided via the central portion, oriented substantially parallel to the radiation and ground face located therebelow, of the patch element.
The aforementioned three-dimensional structure (which is referred to as a “three-dimensional” structure because it has a significantly greater material thickness or material height than metal plates or metal foils used according to the prior art) does not necessarily require the entire member to be configured as what is known as a volume member or the aforementioned peripheral edge necessarily to encircle the entire edge portion of the patch structure. Edge or web elements provided only in certain sections are also sufficient. Recesses or even, for example, a concave deformation of the patch face facing the radiation face located therebelow may also be provided in the patch face itself. However, recesses, which protrude, for example, from the peripheral edge into the patch face, may also be formed in the patch face.
Also possible is the use, for example, of a dielectric member which is made from plastics material and is coated with an electrically conductive layer. On use of a “volume member” of this type having a thickness or height of, for example, more than preferably 0.5 mm or 1 mm, in particular more than 1.5 mm, said member should be provided, at least on a side located parallel to the radiation face, preferably on the side located adjacent to the radiation face and on its peripheral wall or edge portions, with an electrically conductive layer. The upper side, remote from the radiation face of the patch antenna, of the electrically non-conductive member may also, if required, be equipped with an electrically conductive layer.